1. Field of Invention
The present invention relates to a light emitting device and a method of manufacturing the same. More particularly, the present invention relates to a nitride based semiconductor light emitting device with enhanced luminous efficiency and brightness and a method of manufacturing the light emitting device.
2. Description of the Related Art
A light emitting device refers to an element in which minority carriers (electrons or holes) injected using a p-n junction structure of a semiconductor are produced and certain light is emitted due to recombination of the carriers. A light emitting source is formed from any one or combination of compound semiconductor materials such as GaAs, AlGaAs, GaN, InGaN and AlGaInP, so that a variety of colors can be implemented. For example, a red light emitting device may be formed from GaAsP or the like; a green light emitting device may be formed from GaP, InGaN or the like; a blue light emitting device may be formed using an InGaN/GaN double hetero structure; and a UV light emitting device may be formed using an AlGaN/GaN or AlGaN/AlGaN structure.
In particular, GaN has a direct bandgap of 3.4 eV at a normal temperature and a direct energy bandgap of 1.9 eV (InN) to 3.4 eV (GaN) or 6.2 eV (AlN) by combining with a substance such as InN or AlN. Thus, GaN is a substance with great applicability to an optical element due to its broad wavelength range from visible light to ultraviolet light. Since the wavelength can be adjusted in such a manner, full-color implementation can be made by means of red, green and blue light emitting devices with a short wavelength range, so that the applicability to a general illumination market as well as a display device market is expected to be greatly increased.
Light emitting devices have characteristics of lower power consumption, longer lifespan, better installation in a narrow space and stronger resistance against vibration as compared with existing bulbs or fluorescent lamps. Since the light emitting devices are used as display devices and backlights and have superior characteristics in view of the reduction in power consumption and the durability, many studies for applying the light emitting devices to a general illumination field have been recently conducted. In the future, their applicability is expected to extend to a backlight of a large-sized LCD-TV, a vehicle headlight and general illumination. To this end, it is necessary to improve luminous efficiency of light emitting devices, solve a heat dissipation problem, and achieve high brightness and output of the light emitting devices.
Many techniques for enhancing the performance of light emitting devices have been currently developed. There are various indexes indicating the performance of light emitting devices, such as luminous efficiency (lm/W), internal quantum efficiency (%), external quantum efficiency (%) and extraction efficiency (%). The extraction efficiency is determined as a ratio of electrons injected into the light emitting device to photons emitted to the outside of the light emitting device. That is, the light emitting device becomes bright as the extraction efficiency becomes high. Since the extraction efficiency of the light emitting device is much influenced by the shape and surface pattern of a chip, the structure of a chip and a packaging type, careful attention should be paid when designing the light emitting device.
FIG. 1 is a sectional view showing a conventional light emitting device with a horizontal structure.
Referring to FIG. 1, the light emitting device comprises a substrate 1, an N-type semiconductor layer 2 formed on the substrate 1, an active layer 3 formed on a portion of the N-type semiconductor layer 2 and a P-type semiconductor layer 4. That is, after the N-type semiconductor layer 2, the active layer 3 and the P-type semiconductor layer 4 have been sequentially formed on the substrate 1, predetermined regions of the P-type semiconductor layer 4 and the active layer 3 are etched to expose a portion of the N-type semiconductor layer 2. Then, a predetermined voltage is applied to top surfaces of the exposed N-type semiconductor layer 2 and the P-type semiconductor layer 4.
FIG. 2 is a sectional view showing a conventional light emitting device with a flip chip structure.
Referring to FIG. 2, the light emitting device comprises an N-type semiconductor layer 2, an active layer 3 and a P-type semiconductor layer 4, which are sequentially formed on a base substrate 1. The light emitting device further comprises a submount substrate 5 onto which the base substrate 1 is flip-chip bonded using metal bumps 8 and 9. To this end, the N-type semiconductor layer 2, the active layer 3 and the P-type semiconductor layer 4 are sequentially formed on the predetermined substrate 1, and portions of the P-type semiconductor layer 4 and the active layer 3 are etched to expose the N-type semiconductor layer 2 such that a light emitting cell can be formed. Further, the additional submount substrate 5 is prepared to form first and second electrodes 6 and 7 thereon, and the P-type and N-type metal bumps 8 and 9 are then formed on the first and second electrodes 6 and 7, respectively. Thereafter, the light emitting cell is bonded with the submount substrate 5 such that P and N electrodes of the light emitting cell are bonded with the P-type and N-type metal bumps 8 and 9, respectively, to fabricate a light emitting device. Since such a conventional light emitting device with a flip chip structure has high heat dissipation efficiency and hardly has shield of light, there is an advantage in that its light efficiency is increased by 50% or more as compared with a conventional light emitting device. Further, since a gold wire for driving a light emitting device is not necessary, many applications to a variety of small-sized packages can be considered.
Light produced from a light emitting layer of a light emitting device is emitted from all the surfaces of a chip, and light extraction efficiency is generally determined by a critical angle of light. However, when the conventional light emitting device is etched to expose an N-type semiconductor layer, side surfaces of the P-type semiconductor layer and the active layer are vertically processed such that a portion of light produced within the light emitting device is totally reflected on the etched surface that is processed vertically from a horizontal plane. Then, a considerable amount of light to be totally reflected is not emitted to the outside but dissipated within the light emitting device due to the internal reflection. That is, there is a problem in that luminous efficiency in which electric energy is converted into light energy and the light is then emitted to the outside of a light emitting device is low.